Tyres: Alternatives to KU31s

Guran · Postby **Guran** » Fri Jan 20, 2012 6:45 am

I think you mean Kumho Ecsta LE Sport KU39. I have them on my 135i and agree they're a good tyre in terms of grip and wear rate - but a bit noisy. However they're only available in 17"-19" according to the Kumho website. They're also a bit more expensive than the KU31s.

BadBong · Postby **BadBong** » Fri Jan 20, 2012 8:59 am

Guran wrote:I think you mean Kumho Ecsta LE Sport KU39. I have them on my 135i and agree they're a good tyre in terms of grip and wear rate - but a bit noisy. However they're only available in 17"-19" according to the Kumho website. They're also a bit more expensive than the KU31s.

I was quoted $195 a corner by a Brisbane based supplier 2 months ago for some KU39s in 205/45/16.

Is it worth double the price of KU31s?...

Silvia · Postby **Silvia** » Fri Jan 20, 2012 10:55 am

I'd say no. KU 31's are $170 at KMart.
A quick question while we have the experts together :roll:

I find 1st gear is a bit low and runs out of puff too soon. I can start pretty easily in 2nd.
Plus the fact that 6th seems too low too and would be better as a highway gear. Leads me to think a slightly bigger tyre than the 205/45/16 would be an advantage.
What would be the next size up that is also a common size that would help with this?
NB2002 stock 16" wheels.

project.r.racing · Postby **project.r.racing** » Fri Jan 20, 2012 10:17 pm

tyre rolling diameter doesn't effect rpms. it effects vehicle speed.

JBT · Postby **JBT** » Fri Jan 20, 2012 10:19 pm

...or if the true speed stays constant, the RPM varies. :wink:

PaulF · Postby **PaulF** » Fri Jan 20, 2012 10:21 pm

project.r.racing wrote:tyre rolling diameter doesn't effect rpms. it effects vehicle speed.

It will affect road speed relative to engine speed, effectively changing the gearing of the car - just like putting in a different rear end ratio.

JBT beat me to it.

project.r.racing · Postby **project.r.racing** » Sat Jan 21, 2012 9:20 am

FFS, I give up. There is always some old dude that thinks they know better than others.

JBT · Postby **JBT** » Sat Jan 21, 2012 9:59 am

Correction...he knows he knows better.

project.r.racing · Postby **project.r.racing** » Sat Jan 21, 2012 10:39 am

And there lies the problem I guess? The distance between knowing your right and actually being right can be massive for anyone.

Until Silvia posts again and confirms what here actually wanted, no one know nothing.

I took his post as a gear ratio issue in various gears. And you both have taken the issue as a rpm vs vehicle speed issue.

mazdarati · Postby **mazdarati** » Sat Jan 21, 2012 10:42 am

Guran wrote:I think you mean Kumho Ecsta LE Sport KU39. I have them on my 135i and agree they're a good tyre in terms of grip and wear rate - but a bit noisy. However they're only available in 17"-19" according to the Kumho website. They're also a bit more expensive than the KU31s.

No No,
http://www.tirerack.com/tires/tires.jsp?tireMake=Kumho&tireModel=Ecsta+SPT
Just the Sport (SPT) model.

I've got them in a 195/50/R15

JBT · Postby **JBT** » Sat Jan 21, 2012 10:54 am

project.r.racing wrote:And there lies the problem I guess? The distance between knowing your right and actually being right can be massive for anyone.

Until Silvia posts again and confirms what here actually wanted, no one know nothing.

I took his post as a gear ratio issue in various gears. And you both have taken the issue as a rpm vs vehicle speed issue.

The "problem" is that your statement prior to this was:

project.r.racing wrote:tyre rolling diameter doesn't effect rpms. it effects vehicle speed.

and that is clearly incorrect regardless of the age of the contributor.

project.r.racing · Postby **project.r.racing** » Sat Jan 21, 2012 11:06 am

no it is not. Tyres do not effect the the gearbox rpms in relation to the engine rpms. But tyres do effect the drive wheel rpms in relation to the engine rpms.
I'm talking about engine to gearbox, and you are talking about engine to wheels.

Silvia talks about his 1st gear being a very high ratio. Regardless of the tyre diameter, it will still from 800rpm to 6000rpm the same, (technically worse is increase diamter by 0.00001%). Tyres will effect the vehicle speed at these rpms. But then Silvia did not mention vehicle speed in that statement did he?

Again maybe it read wrong the post by Silvia, so just gotta wait until he comfirms what he was actually wanting right?

I read it as, 1st is too high, 6th is too low. I don't think changing tyres will help as smaller tyres will make 1st even higher, and bigger tyres will make 6th even lower.

project.r.racing · Postby **project.r.racing** » Sat Jan 21, 2012 11:18 am

mazdarati wrote:
Guran wrote:I think you mean Kumho Ecsta LE Sport KU39. I have them on my 135i and agree they're a good tyre in terms of grip and wear rate - but a bit noisy. However they're only available in 17"-19" according to the Kumho website. They're also a bit more expensive than the KU31s.

No No,
http://www.tirerack.com/tires/tires.jsp?tireMake=Kumho&tireModel=Ecsta+SPT
Just the Sport (SPT) model.

I've got them in a 195/50/R15

KU31s, they can be had for $80ea on ebay in that size.

The KU31s is what this whole thread is about, or at least replacing them with some other manufacturer/model. Which seems to be a difficult task as the conversation seems to keep returning back to KU31s and there awesome price and handling.

JBT · Postby **JBT** » Sat Jan 21, 2012 12:00 pm

project.r.racing wrote:Tyres do not effect the the gearbox rpms in relation to the engine rpms.

Correct. However, one assumes that the car will be dríven on a road and not just sit on blocks, stands or a hoist with the bowels being revved out of it. So, considering engine RPM in isolation from actual road speed or indicated speed is irrelevant.

project.r.racing wrote:But tyres do effect the drive wheel rpms in relation to the engine rpms.

Incorrect. The wheels will spin at precisely the same RPM for a given engine RPM and the speedometer (if the speedometer output gear in the gearbox has not been changed) will indicate precisely the same speed. However, the actual (true, real) speed of the vehicle will differ for a given RPM if the wheel/tyre rolling diameter is changed.

project.r.racing · Postby **project.r.racing** » Sat Jan 21, 2012 3:55 pm

JBT wrote:
project.r.racing wrote:Tyres do not effect the the gearbox rpms in relation to the engine rpms.

Correct. However, one assumes that the car will be dríven on a road and not just sit on blocks, stands or a hoist with the bowels being revved out of it. So, considering engine RPM in isolation from actual road speed or indicated speed is irrelevant.

I personally use engine rpms as my shift points and not road speed/real speed to know when to change gears in motorsports I do. So it is relevant to me. Maybe you should try it sometime? Might keep you car in a more powerful rpm range and get you faster time...

JBT wrote:
project.r.racing wrote:But tyres do effect the drive wheel speeds in relation to the engine rpms.

Incorrect. The wheels will spin at precisely the same RPM for a given engine RPM and the speedometer (if the speedometer output gear in the gearbox has not been changed) will indicate precisely the same speed. However, the actual (true, real) speed of the vehicle will differ for a given RPM if the wheel/tyre rolling diameter is changed.

Happy? It was a typo.