Lotus Elan Central

by **Sy V** » Fri 25.11.2005, 06:36

After I fitted my big brakes I had to put spacers on the front hub carriers to allow the (15" at that time) wheels to spin freely. The effect was tram lining and this was a major driving force propelling me down the 16" option and the thankful removal of the spacers and the return to 60mm offset.

by **Dovey** » Fri 25.11.2005, 17:44

Reducing the wheel offset will tend to move the contact patch outboard of the steering axis...

Yup. That's why wheel bearings may be a problem. Probably the biggest downside is the turning circle is pants which isnt good for parking. But I can live with that as I have crappy escort for shopping in.

another effect of changing offset is that the car will move vertically as the wheel is turned

Not so sure about that though

by **Dovey** » Fri 25.11.2005, 17:55

205's are standard on the rear

I respectfully suggest that they are on s2's but not on se or na models

by **Sy V** » Fri 25.11.2005, 17:57

Nope, sorry.

by **F1 LOTUS** » Fri 25.11.2005, 19:13

Dovey wrote:
Reducing the wheel offset will tend to move the contact patch outboard of the steering axis...

Yup. That's why wheel bearings may be a problem. Probably the biggest downside is the turning circle is pants which isnt good for parking. But I can live with that as I have crappy escort for shopping in.

another effect of changing offset is that the car will move vertically as the wheel is turned

Not so sure about that though

Exagerate the geometry... and you'll get an idea of what's happening...

You can simulate this with a cocktail sausage on a stick :shock:

...The tyre is cylindrical (not spherical) like the sausage, the stick is the steering axis...Now there is only one position of the stick (steering axis) where the sausage will leave a nice circular greasy mark (contact patch) on the tablecloth, and that is with the stick vertical which in geometric terms would be zero caster and zero camber! Roll the sausage back so the stick is inclined like a motorcycles front fork and you're simulating caster...now turn the stick (steering) and you'll see how the car would lift, no? Add some camber by inclining the stick along the sausages' axis and you'll be drawing greasy arcs on the table...geddit

Hungry work geometry :!:

by **Nige** » Fri 25.11.2005, 20:14

205s all round on all Elans, NA's, SE's and S2's as standard.

by **DeeAitch** » Fri 25.11.2005, 20:52

The wheel offset affects 'scrub radius'. Look here http://www.familycar.com/alignment.htm for an easy to understand explanation of this and other suspension geometry. Quite a science - It will make you realise why Lotus are so good at it

As for 16" v 15" a quote from Car magazine August '94 "the larger wheel & tyre .... weigh 4lb more.... the damper settings have had to be changed to suit the extra mass. I get the impression (John, ex Lotus F1 driver & Engineer on the M100) Miles is somewhat pained by the concession to style"

by **Dovey** » Sun 27.11.2005, 09:30

I see. Thanks for that. Three things leap to mind:
1 My geo was wrong when I bought the car and before I started messing with it
2 In my defence no else noticed my rear tyres being the wrong size either. Not even my local lotus dealer.
3 My tyres are not sausage shaped :wink:

I think increasing the offset will exaggerate any vertical movement already there rather than be the cause. I would like to think there isn't any, of course in engineering there is no such thing as an absolute, but I like the 'Trini Lopez' approach.

by **F1 LOTUS** » Sun 27.11.2005, 19:45

Dovey wrote: but I like the 'Trini Lopez' approach.

Go on then, I'll bite: what does it mean

by **Dovey** » Mon 28.11.2005, 02:35

Trini Lopez was the guy who sang that song "If I had a hammer". Check out www.trinilopez.com to book him for a local town hall performance and impress your dad :roll:

by **Houdini** » Wed 11.01.2006, 20:57

I think Lotus' intention with the front steering geometry was to put the steering axis close to the centre of the tyres contact patch, all part of the effort to reduce front wheel drive torque steer and kick-back etc? Reducing the wheel offset will tend to move the contact patch outboard of the steering axis...

To get some understanding of the effect of this it helps to exagerate the offset...with the steering axis in the centre of the contact patch the wheel would turn in the same way that a coin spins on edge
With the steering axis offset from the tyre contact patch, the wheel will sweep in an arc fore and aft similar to a soapbox axle that has a single bolt in the middle of the cart

If you now consider the outside effects on the tyre from the road, you can probably visualise how this might be felt back through the steering wheel?
Also, as the car is cornered harder the tyres' contact patch will move further outboard towards the sidewall and exert greater leverage back through the steering (heavier).

Obviously the above is a simplified explanation of perhaps just one of the effects, another effect of changing offset is that the car will move vertically as the wheel is turned ...

Suspension geometry is pretty complex and Lotus Engineering are recognised as being a leading authority on the subject, which is why most of the worlds car manufacturers call upon their expertise

I'm far from being an expert in anything but I did some online research and found that negitive scrub radius on a front wheel drive car reduces torque steer and in a cornering situation the side wall flex will in effect move the scrub radius outboard slightly getting it close to zero. I also found that on race cars having a slightly positive scrub radius is a good thing as it gives the driver better feedback.

Our M100's have a 10.5 degree steering axis inclination and -3mm scrub radius. Now if you put a +45 offset wheel on your car you will be changing your scrub radius to + 12mm and will feel the effect be creating more torque steer on launch and you'll have a harsher ride. This may not be a big problem as not many Elan drivers are actually drag racing. On a street car cornering is probably not a hugh deal either, but may be noticable as you drive harder and will be an issue for sure on the track. you can get some of that scrub radius back through alignment and by having a taller tire. So lets say I were to go to a 17x7 50mm offset team Dynamic wheel from a 16x7 60mm offset stock federal wheel. Given the stock tire size (205-45/16 ), and going to a 17 inch tire (215-40/17) my tire diameter will increase by 13mm and tire radius will increase by 6.5mm and using a little math and trig my scrub radius will change from -3mm to +7mm because of the tire and I will gain back approx. 1.2mm because of the increased tire diameter giving me +5.8mm scrub radius. Because of the shorter stiffer sidewall I may also gain a little more back when cornering. So is +5-6mm scrub radius too much for spirited driving? I don't know, maybe someone else does and I'd like Brian or someone else to chime in. if I don't want to use my stock wheels on the track it might be worth trying a set of 17x7 50mm offset wheels.

by **F1 LOTUS** » Thu 12.01.2006, 09:06

Turbocharger wrote:
So is +5-6mm scrub radius too much for spirited driving? I don't know, maybe someone else does and I'd like Brian or someone else to chime in. if I don't want to use my stock wheels on the track it might be worth trying a set of 17x7 50mm offset wheels.

Russ, I don't have any practical experience of this

Sy commented that he could notice the difference when he spaced his wheels out though?

by **Sy V** » Thu 12.01.2006, 09:29

Confirmed.
When I first put my big brake kit on (with 15" wheels) I had to add 6mm spacers on each hub to accommodate the calipers.
The car tramlined like buggery.

by **jordizr1** » Fri 20.01.2006, 08:20

When I bought my car it had 17x7 et45 wheels, after reading this I see these wheels are out of specs.
I have access to a wheel builder that can build custom wheels (lots of designs) in alloy or magnesium with virtually any et (offset).
www.braid.es
My question is, if I want to keep 17" wheels (for the looks) what size of wheel would be the closest to factory specs? I guess it would be 17x7 et60 with 205/40/17 tires, am I wrong?

by **Sy V** » Fri 20.01.2006, 09:52

Interesting site, with a number of nice examples.

by **jello** » Thu 30.03.2006, 07:10

Anyone here actually a wheel expert?? I'm not, but I was thinking on this - what if one were to buy an aftermarket wheel - say a 17X7 with a 45mm offset - take it to a friend with a lathe, and have the center machined down by 5 or 10 mm and the lug bolts cut off 5 or 10 mm accordingly. Wouldn't that take care of the offset, or is there a structural rigidity that will be violated there?? Most of the wheels have a fairly large center section, and it seems to me that the mating surface, and the flare on the lug bolt are what holds it to the hub. As long as those aren't interferred with (i.e. mating surface remains flat, lug bolt flare can mate up to the wheel), would the wheel/system be weakened??

Phil

by **Houdini** » Fri 31.03.2006, 00:43

If there is enough stock and it can be done without endangering the structual integrety of the wheel then I don't know why not. Team Dynamics machines every wheel when you purchase it to the offset you want but they won't machine farther than 50mm so you're still 10mm shy. If i had the money I'd have Kodiak build a set of wheels. Correct offset, width, and extremely light.

by **Guest** » Mon 03.04.2006, 04:54

Well I talked to my local wheel supplier, and I looked at some 17X7 wheels (although they were 40mm offset). One couldn't mill off 10 or 20 mm, because there isn't that much material there - I found htat by looking at the 40mm offset wheels today. Second, the wheel/tire shop has been checking for some 60mm offset wheels for me. They can order some custom made from an outfit like Weld Racing, but they're extrordinarily expensive. Further, they are really just for show, and don't generally get DOT approval for the road. Apparently teh 60 offset puts a lot of stress on the wheel structure, and they break. So, if you have OEM wheels - don't worry be happy. If you want aftermarket wheels, expect to change offsets.

Phil

by **Doug** » Mon 03.04.2006, 07:14

well you wouldn't 'mill' material off the usual wheels to get them to +60mm offset; you'd have to throw a spacer between the rotor and the wheel--then the bolts or studs would be too short; then you'd need new studs, etc, etc

by **Elanlover** » Mon 17.04.2006, 21:29

As usual, I'm late to the party on this issue but................

Was curious about the subject so I did Googled for offset tires with the Elan specs and got this website.

http://www.rojawheels.com/resources/top ... e=acuransx

Look over the NSX wheel specs. 17 x 7 with a +55 offset is one of the specs that's standard for this car with some nice looking rims too. There's other cars here too that have similar specs.

Lotus Elan Central

wheels

ideal 17 wheels?

wheel experts??

60mm offset

Who is online