OFFSETS ! 15" & 16" & 17"

[thewheelrestorer]

Hi,

Quickie really, can somebody confirm the original 15" wheel offset? Is it +ET60 and the Rim width 6.5" ?
Also the fed 16" is this a 7J ? and again ET60? and the S2 wheel a 7J ? and ET60

Just starting to work my brain on a solution and also what tolerance will really not make a difference dispite the purists rumours.

Who has 17" Rims out there ? and if so what offset are you running?

Also did you change from a 15 to 17" ?or a 16 to 17" and if so did you notice any plus or minor points in driving and handling ? Also any differentce in wear characteristics on the front tyres in particular?

Looking forward to your replies.......

[XiPHiAS]

I HAD 17" ET45 and it sucks ... now I'm running again on the OE 15" (SE) wheels.

The car feels a lot better on handling, but on fast long corners the Elan gave me an unsafe feeling (it felt like the car lifted in the long fast corners).

But, before I buy other wheels, I want to do the KW suspension and after that I will do some tests to see what happens if I fit weels with a lower ET than 60. For me the wheels of the Elan are extremely deep into the car. For a visual better look, ET45 is better because the wheels will become in line with the weelgaps, and thats much nicer.

But I prefer technical tuning above aerodynamics and looks. So IF I modify things on the Elan they NEED to be better!

[thewheelrestorer]

Interesting that you had an strange stability feel at speed and also with a wider track, which can "Jack" up the diagonally rear corner and make the car feel like it is tipping more at the front, did it feel like the car wanted to spin round?

The 17" wheels you had, what was the width ? 7" , 7.5" , or 8" ?

ciao,

[thewheelrestorer]

67 Views and nobody can tell me the offsets of the 3 wheels types !!!

Come on........somebody must know ??

I know then S2 is Et60 on my Car, but I'm not sure about the 15 " and fed spec ? ?

Anyone??

[paulwatkins]

I dont know off the top of my head!

But looking at the Lotus Elan M100 Service Notes reveals the following

standard alloy 15in - 6.5J x 15 H2E 60
standard alloy 16in (info from 1990 so FED) - 7J x 16 H2 ET 60
winter steel( ) 6J x 14
temporary spare 3.5J x 14 H2

Inset - standard alloy +60mm


Anything else you want me to look up in the manuals while I have them open?

[thewheelrestorer]

Thanks Paul, That'll do.

I'll continue with my research, and get back asap hopefully on some solutions to this large offset problem.
Regards

[Elanlover]

I had custom 17x7 wheels made with the corrct +60 offset recently. Popular belief seems to state that a +/- 20% change in the offset is tolerable. Obviously, the closer you can get to the stock +60 offset the better. There are very few choices in a 17 inch wheel that come close to +60 off the shelf. None at all at exactly +60. The closest I saw in all my research was about +53 and you wouldn't want to go less than +48 if you follow the conventional wisdom.

All this information can be found in the forum. Try a search for wheel offset or similar.

[thewheelrestorer]

Hi,

Out of interest was the Et53 an after market wheel or a OE vauxhall wheel ?

I think the BMW Mini route may have some potential, I've got a set on the way which we will machine the centre bore from 56.1 to 56.6mm and I'm also hoping the centre hub will have enough meat on it to also be reduced and machined to gain more offset. Hopefully if the machine works pans out as planned I may have an offset of et54 which is as close as I can find at the moment, but I've also got another set of Japanese "Rays Engineering" 17" 3 piece splitrims where the centre can be bolted on inner and outer flange hoops, this should also give me a high offset but I'm unsure how high until I get round to calculating it.............

ciao,

[Elanlover]

Hi,

Out of interest was the Et53 an after market wheel or a OE vauxhall wheel ?

I think the BMW Mini route may have some potential, I've got a set on the way which we will machine the centre bore from 56.1 to 56.6mm and I'm also hoping the centre hub will have enough meat on it to also be reduced and machined to gain more offset. Hopefully if the machine works pans out as planned I may have an offset of et54 which is as close as I can find at the moment, but I've also got another set of Japanese "Rays Engineering" 17" 3 piece splitrims where the centre can be bolted on inner and outer flange hoops, this should also give me a high offset but I'm unsure how high until I get round to calculating it.............

ciao,

The +53 wheel was a Work wheel (if you need the details its all the info's in the forum - just do a search for it ). There were other after market wheels I found with offsets of +50 and +48 as well. Nige has fitted the Mini wheel after making the centre bore larger (his findings are also in the forum somewhere). I didn't think the Vauxhall wheels were even close to +60

[thewheelrestorer]

No your right the biggest Vauxhall offset I've seen I think was et52 which was probably on a 15" rim, some vauxhall wheels are et49.

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OFFSETS:

I've done a few sketches to illustrate the amount a 15" and 16" S2 wheel stick outwards and inwards of the car both with et60::


If I'm correct the original 15" wheel is a 6.5" width and the S2 16" a 7"J.


This change from the 15" orignal to a 16" S2 wheel, makes the S2 wheel sticks outwards by 6.5mm more than the 15" did.

Also the S2 wheel is further inboard by 6.5mm (This is where the extra 1/2" is distributed, either side of the centre line)


Does anyone know if the SE and S2 geometry and / or hub positions differ ?


If they are exactly the same then Lotus would of calculated,tested? and approved the difference as above for the S2 wheels with the wider 7" rim (16" diameter) and obviously the extra 6.5mm either side did not have any major adverse effect on the handling.

This extra 6.5mm sticking out and inwards may of been the limit ?

But if not ? and this difference could be added on again? another 6mm sticking out (total 12mm) then an offset of that rim could be reduced to et48.

EG
A 17"rim with a 7" width and an ET 48. would stick out 12mm more than an S2 (The length of my little pinky finger nail!) which may make an adverse difference to the handling, tyre wear and bearing life? or maybe not ? ?

This same rim is also 5mm less inboard than the original 15" (6.5" width) so clearance is not an issue, although the outer wheelarch may be close for clearance as the wheel sticks out 12mm more than the S2.

I've found a Mini Wheel set which is ET48, and I'm hoping I can at least machine off 2mm, maybe 3 or 4 mm from the centre hub and raise the offset to et50, 51, or 52.

I'm keen to try this and see how it feels, I may also dabble with tyre sizes a little like ektrolley boy but not as drastic.........

215/40/17 is only 2.18% bigger diameter than the S2 (205/45/16) size, this will make each gear taller which is not really ideal, (I would personally rather have a shorter gearing for maxiumuim acceleration) but when the speedo reads 70 the actual speed is a little more (71.5mph) which may not be an issue.

The main reasoning for trying this size is because I think from previous experience a bit extra tyre flex from the 10mm extra width will help the ride (As the sidewall is taller) and I think possible help the handling.

Sometimes a square wide rim on a narrow - ish tyre has no a lot of give and is sometimes makes the steering too sharp, also cosmetically it will fill out the wheels arches a bit more, as I do sometimes look at the car and think the arches are huge and the gap massive !

I can also get Goodyear F1 tyres ion this size for £89 each+ vat which is quite good for a high performance tyre.

If anyone wants to try these I'll only charge you 15% VAT from Monday !!

[ailwyn]

I don't know what they did or for what reason, but I believe Lotus tweaked the suspension for the S2 wheels.

[Jimmer]

This is my understanding too. Worth checking out Rota's range. They have a good selection of suitable 16" and 17" with offsets up to 53mm if I remember right.
If enough like one style I may try talking them into making a batch with 60mm offset - they're based in the Philippines and my girlfriend speaks the language which could help.
http://www.rotawheels.com/

[thewheelrestorer]

Sure, brand new wheels ones would be a nice, but could be xpensive?

Also it's all a matter of taste for the car user what style they like, and also what looks right on the car.

Sometimes second hand wheels can be good value, especially if they need repainting as this is our expertise, then they will look as new and in reference to the mini wheels if this avenue is possible with a litle machining some of the styles are quite nice.

The set I'm hoping to fit are (BMW Mini ) AC Schnitzer 17" 5 spoke design which I think will look good, I may paint the centre a Satin or matt ? Black and have the outer rima nd lip diamond cut polished, then the whole wheel gloss lacquered? we#ll see how they fit first.

[tweetdriver63]

I don't know how you're calculating all the measurements/etc (comparing the amount the different rims stick out, etc), but in this thread, you'll find a link to a really convenient online calculator that will show you everything you could ever want to know. You put in the original rim and tire sizes, including offset, then you put in the info for the new set, and it will give you everything. Take a look. It might make some things easier for you in your search.

[thewheelrestorer]

Sure I've seen this thread , but clear is to sketch the cross section on a sheet of paper, then sketch other rim sizes etc, and you can see with your own eyes what 6mm or 12mm actually looks like, which I think gives a good understanding.

What I'm a little surprised at is the difference between the 15" and 16" which nobody that I've heard doen't see as a problem, maybe as previosuly mentioned this difference may be the maximum that Lotus would allow, but if you change the wheel offset and rim width again by the same amount it doesn't look that different on paper, but in realilty driving may highlight some differences!

If you think about most cars have the same scenerio, like a BMW 316i on skinny 6" wide 152 diameter rims, can be changed for 8x18" which will stick inwards and outrwards
by an inch each way, and this is done on thousands of cars without any major problems.

I will say I once owned a 1.6 DOHC MR2 1986 and it originally 185/60/14 size, which I changed for 205/45/16, but driving it was awful !! The rims and tyres were toobig and wide for it, the steering felt too heavy and there was too much scrub going on, it wouldn't turn a corner nicely, the extra rim and tyre width especially at the front was rubbish as there was no weight at the front (Rear engine). I put the olf 14" wheels back on with the best sticky Yokohama rubber and it was fantastic in comparison........So I'm well aware changing tyre widths and or sidewall profile ratio's and wider rims can be a nightmare!

[Mike_H]

The way I see it is that both the 15" and 16" wheels hold the tyre in exactly the same position and both maintain the scrub radius of -3mm which is crucial to the handling of the car. Thanks for spotting my error bob.

[bobbrown]

I agree with maintaining the scrub radius but I think it is -3mm not zero or so my service manual states, so small change to the wheel offset will effect this and have an effect on the handling.

There will also be differences in tyre diameter up to 5% due to tolerances in the tyre specification from one manufacturer to another.
Plus 4% for tyre wear (new to worn to minimum) probably part of the reason the speedo has an allowance of 10%

Bob

[thewheelrestorer]

Interesting thoughts especially on the tyre wear and size tolerances............

: I've seen these diagrams before they are quite good at viewing the wheels new position when the offset is changed.

I wasn't sure if the backspace and front space (Not shown)made a difference to the scrub radius?

if this is -3 as bob mentioned, is this 3mm inboard from the centreline?

I'm pressuming your 1st diagram is a sketch as the centreline runs through the middle of the brake disc?

So if I'm understanding this calcution correctly as long as the space from the hub mounting face to the wheel mounting face is 60mm, the angle from the top ball joint lines up?
and any front or backspace doesn't make a difference?

Only I would of thought a 8" Rim with a et60 would stick inboard and outboard so much it would make a difference to the handling ??

Which is why when I measure on paper the difference between the 15" (6.5" width) and 16" (7" Width) rims there was a difference in the front and backspace and this I thought must of been an acceptable difference that lotus allowed to happen.

Very different I know.............. but on Racing Karts, if we want to loose grip (Sounds funny but it 's one of the only car sports where you can have too much!!) we move the front or the rear wheels outwards.

In the case of the front, when the fronts go further out and the Kart turns right, the left front wheel "Jacks" up the opposite diagonal right rear and lifts it off the floor by .5mm or so. This allows the Kart to turn as it has a wide rear track and no differential (Solid rear axle).

I would of thought for example half inch (12.2mm) sticking in board and outboard from a 7.5" Rim would affect the handling even if the offset was ET60?

It's Saturday morning.......I've been up since 6.00am and driven for 2 1/2 hours on the M6 in freezing Fog............so I may head may not be too clear on this..........but I think it's quite a complex subject...

[bobbrown]

Negative values are inboard of the centre of the tyre contact patch so -3mm is inboard.
A lot of things can effect the scrub radius but width of tyre/rim on its own is not one of them.
The steering axis inclination or king pin inclination is a line draw through the centre of the two ball joints to the ground or in the case of a MacPherson strut from the centre of the top mount through the lower ball joint to the ground.
There are a lot of things to take into consideration here and sticking to the standard offset and rim/tyre diameters will help to keep the scrub radius with in limits.

I think the fact that the centreline runs through the centre of the disc is purely coincidental.

As for trying to compare a kart to a car is going to be very difficult as a kart has no suspension and no differential, the latter means you have to slide the rear wheels to get around a corner.
So to summarise changing the wheel offset and/or overall tyre diameter will change the scrub radius but I can not say if this is going to be beneficial or not but I think the latter is likely to be the case.

Of course if somebody was not too concerned about handling and just concerned about aesthetics then go for the “Carlos Fandago” look but what was the point of buying a Lotus in the first place.
I think a lot of people that buy/sell aftermarket wheels and tyres have very limited understanding about just what they are doing to the cars handling, just because they fit does not mean you should.
All of this is probably why Elanlover went for a custom rim with an offset of 60mm and should not effected the handling at all.


Bob

[Elanlover]

All of this is probably why Elanlover went for a custom rim with an offset of 60mm and should not effected the handling at all.

Yes. In fact, I'm pretty sure I considered every word you spoke here Bob I especially recall thinking about king pin thingies and scrubbing stuff while I was ordering the wheels.

But in general, yes.