How much of a difference does offset make?

[worthyking]

Question: Would a 0.4 lbs weight savings per wheel be more advantageous than losing 12mm of total track width?

What I am wondering is should I go with 41mm offset (Enkei RPF1s) because they weigh 9.5 lbs rather than the 35mm which weigh 9.9 lbs? Is saving 0.8 lbs per axle a benefit if I am losing whatever small degree of cornering stability with a narrower track?

Or am I just being too damned anal about this whole thing?

[seckerich]

Weight difference is in the center and therfore has very little accel/decel mass moment arm. Go with the wider track.

[StephenB]

I would compare cost as well. You could add a 6mm spacer and probably be close to the same weight... right?

[joeg]

Pontiac that baby...wide track!!

[worthyking]

@StephenB No, what I'm doing is going from Kosei K1s (at 13.3 lbs per wheel and 38 mm offset) to Enkei RPF1s. The decision I'm trying to make is whether to go with 35mm Enkeis at 9.9 lbs or 41mm Enkeis at 9.5 lbs.

Will the slightly wider stance be more beneficial or the narrower track with less weight? That's my dilemma.


I would compare cost as well. You could add a 6mm spacer and probably be close to the same weight... right?

[Andy Bettencourt]

Remember, you can always add spacers. If you want the best of both.

[Rabbit07]

Remember, you can always add spacers. If you want the best of both.

And gain the unsprung weight back with the spacer? Come on, really?

[Andy Bettencourt]

And gain the unsprung weight back with the spacer? Come on, really?

Not sure if you are being serious or not but nice aluminum spacers are not heavy. Not super cheap, but not heavy.

[Rabbit07]

Not sure if you are being serious or not but nice aluminum spacers are not heavy. Not super cheap, but not heavy.

Go weigh one of your nice spacers and see if it's less than the .4 lbs he is talking about. Really?

remember it needs to be a 12mm spacer also....

[Andy Bettencourt]

It's .4lbs or about 6 1/2 oz...but 12mm is thick...we only have 10's at the shop. I'll weigh.

[Rabbit07]

Andy,

I use wheel spacers all the time to ; Tune, clear brakes, ect. Never to save weight. It's hard for me to believe you can have the best of both worlds with a lighter wheel that you just added a spacer to? Lighter is faster, wider is sometimes faster, but they don't always fit in the same box.

[Andy Bettencourt]

Andy,

I use wheel spacers all the time to ; Tune, clear brakes, ect. Never to save weight. It's hard for me to believe you can have the best of both worlds with a lighter wheel that you just added a spacer to? Lighter is faster, wider is sometimes faster, but they don't always fit in the same box.

Well you never use them to save weight, obviously. You use them to save money. Money that would have to be spent on a custom wheel in some cases. But if the weight is negligible (TBD by user), then you can save the money, get your offset and not sacrifice too much in unsprung. To me, if your lightweight choice is 12mm off, that is significant (provided you didn't just add a ton of drag). It would outweigh (pun intended) adding 6oz of center mass to the corner IMHO. YMMV.

[worthyking]

I wouldn't go with a smaller offset and then use spacers, as it seems self defeating to me.

But what I would really like the advice on from you guys who have many years of experience is the original question of which is better: 12mm wider track (6mm on each side) or 0.8 lbs less unsprung weight?

Chris, I'm particularly interested in your opinion as I know you have tons of experience in FWD cars on many of the same tracks I run.

[Chip42]

get a 3mm spacer and throw your Kosei's on to see if they fit well. if they do, get the 35s. if they don't, get the 41s and space them out. don't cloud your mind with the very small added weight.

[Rabbit07]

I wouldn't go with a smaller offset and then use spacers, as it seems self defeating to me.

But what I would really like the advice on from you guys who have many years of experience is the original question of which is better: 12mm wider track (6mm on each side) or 0.8 lbs less unsprung weight?

Chris, I'm particularly interested in your opinion as I know you have tons of experience in FWD cars on many of the same tracks I run.

As a tuning tool my personal preference is to always go with the wheel that tucks in the wheel well the best. Then use spacers to play with track. The reasoning is that a wider track wheel can not be made narrower, but the opposite can happen. Say you are at a small tight track with not much straights. You may want to widen the track to gain some handling. Perhaps even widen just the front to help with rotation. On a long course you may want to tuck the wheels a bit for aero. Even though, this is trade off, even at the big track. Wheels sticking out beyond the body work hurts your aero, and your brake cooling. Not many people realize the later.

I am not sure I could answer your question definatively regarding the compromise. Test, Test, and Test again.

This will blow your mind a bit though, I have found that the "heavier" well ballanced car is usually faster than the "lighter" not so well balanced car. Put the weight where you want it so to speak. Track specific of course.

[TS22]

I'm not sure on a Integra, but on a Civic the 41mm offset Rpf-1's fit much better. The 35mm offset will rub on the inner fender liner unless the Fender's Rolled.

[JLawton]

But what I would really like the advice on from you guys who have many years of experience is the original question of which is better: 12mm wider track (6mm on each side) or 0.8 lbs less unsprung weight?

.

I think at our level you would never know the difference. You probably won't even feel a difference going to the lighter wheel (although there WILL be a difference, you just won't be able to feel it)

[callard]

What Jeff said.

[Flyinglizard]

The Spring/wheel rate changes with track change.
Wider softens the wheel rate. 10mm each side is noticeable. 5mm maybe not.
If you want to figure wheel rate VS spring rate. Extend the strut centerline down to the ground. mark the center. Mark the center of the tire contact patch.
Measure the length of the lower control arm pivot, to the tire center and to the strut center. Divide the shorter into the longer.
Most are 95% or so.

Wider track also promotes weight transfer onto that tire sooner.
IMHO, MM

[Matt93SE]

I've got wheels everywhere from +45mm offset to +15mm offset, 14lb to 24lbs each. the only time I can tell a difference is when I go from my 14lb wheels to my 24lb wheels, and the car is a bit slower.
otherwise, I can't tell a difference between the offsets or a 1-2lb/wheel weight difference.

If you can feel that in your driving, then you're a much better driver than me.

[Wreckerboy]

Wheels sticking out beyond the body work hurts your aero, and your brake cooling. Not many people realize the later.


Please explain this, as I am not following the logic. TIA.

[Rabbit07]

One other compromise here is Scrub Radius. Don't forget that!

On the Areo and Brake Cooling, the air gets disrupted with the rolling tire. If the Tire/Wheel is tucked the air moves past it on the outside aiding in evacuating the hot air from the brakes.

[ShelbyRacer]

Chris,

I'd actually think that having the face of the wheel roughly even with the body of the car is best for evacuation. Having the fast moving air provide the low pressure would induce the best airflow, providing you have a high pressure area as a source. Having the wheel tucked in would tend to generate a turbulent null (cowl induction anyone?), which would provide pressure much closer to atmospheric, probably tending towards a back flow to the underside of the car. Again, all this depends on the aero package as a whole...

[shwah]

One other compromise here is Scrub Radius. Don't forget that!

On the Areo and Brake Cooling, the air gets disrupted with the rolling tire. If the Tire/Wheel is tucked the air moves past it on the outside aiding in evacuating the hot air from the brakes.

Which is why you should use the air dam allowance to cover as much of the wider track tires as possible.

I have taken the widest track I can get approach. 1" spacers in the front with ET13 wheels vs. stock ET35. My car is lb/hp challenged for my class, which is pretty much a momentum class anyhow - so I tend to choose trade-offs in favor of cornering.

The scrub radius stuff is a valid concern, but IMO when you are working the tire at an appropriate slip angle, it is less of an impact than when there is static friction between tire and road. Bump steer probably causes more issues...

[Flyinglizard]

Scrub only counts when both front tires are on the ground.

[quadzjr]

Scrub only counts when both front tires are on the ground.

I think we should assume that atleast for the majority of the time we plan to keep the front tires on the ground. :)

[shwah]

I think we should assume that atleast for the majority of the time we plan to keep the front tires on the ground. :)
You would be surprised how often they are not.

More importantly how often the inside tire has very little load and thus very little friction to share with the rest of the situation.

At least if you are running a solid diff.

[Flyinglizard]

Chris has it. If you are going fast with a locked diff, the car is like a two wheeled device. The inners are off of the ground. MM

[betamotorsports]

Track is one of the components of lateral load transfer. Its far more important then 1.2 lbs of unsprung weight.