DIR Return Create A Forum - Home
---------------------------------------------------------
CycleKarts GB
HTML https://cyclekartsgb.createaforum.com
---------------------------------------------------------
*****************************************************
DIR Return to: Build journals
*****************************************************
#Post#: 2627--------------------------------------------------
Re: Bugatti Type 37 Build - tyre size comparison
By: StefanN Date: July 18, 2020, 3:36 am
---------------------------------------------------------
The smaller tyres change the diameter of the wheels from 600mm
to 570mm. That'll give a 5% change in gearing. Changing just
the back tyres for now will increase the caster at the front by
0.5 deg.
A rear wheel with the 3.25" tyre weighs in at 6.2kg. With the
2.50" tyre it weighs 5kg. To me, that's a surprisingly large
difference.
#Post#: 2628--------------------------------------------------
Re: Bugatti Type 37 Build
By: RhysN Date: July 18, 2020, 12:08 pm
---------------------------------------------------------
What is the main aim for making the change. Those bigger tyres
in some makes are a whole lot heavier, but that surprises me
too. Is it because you are going from a full motorcycle tyre to
more of a moped one?
#Post#: 2629--------------------------------------------------
Re: Bugatti Type 37 Build
By: StefanN Date: July 19, 2020, 3:07 am
---------------------------------------------------------
The aim of the changes is to get the car handling in a way I
enjoy, and have fun experimenting along the way. With the
current setup I have both rear wheels keyed to the axle. Also
the weight distribution is a little too much to the rear. As a
result it understeers badly and with the extra grip it’s
difficult to get a controlled drift.
The other effects (weight, ratio, caster) I’ve noted above are
just observations and the caster difference will be temporary; I
just wanted to check I wasn’t get an unhelpful effect from
running different size tyres during initial testing.
Other possible tweaks I may try are:
- Dropping the seat even further
- Moving seat bottom and pedals forward
- Add weight at the front
- Playing with track width at the back (narrow like the GN’s or
wider for more stability)
#Post#: 2630--------------------------------------------------
Re: Bugatti Type 37 Build
By: RhysN Date: July 19, 2020, 4:52 am
---------------------------------------------------------
For me it's the fiddling that appeals the most, and your
analytical approach interest me.
Have you tried playing with tyre pressures? They do have a huge
effect on the CK.
The narrowing of the rear track, I am sure, would be the most
beneficial of those you mention. AFN did loads of experimenting.
The GN and later Fraser Nash always had solid drive axles, and
narrower rear track.
One change at a time :)
#Post#: 2631--------------------------------------------------
Re: Bugatti Type 37 Build
By: StefanN Date: July 19, 2020, 5:04 am
---------------------------------------------------------
Yes did lots with tyre pressure and it helped, but not enough.
I have a suspicion that pushing the rear tyre pressure up might
have contributed to my spokes loosening at the end of last year.
#Post#: 2632--------------------------------------------------
Re: Bugatti Type 37 Build
By: ChrisS Date: July 19, 2020, 5:11 am
---------------------------------------------------------
What's your weight distribution like? Mine is 70kg rear, 35kg
front, so exactly 2:1.
#Post#: 2633--------------------------------------------------
Re: Bugatti Type 37 Build
By: RhysN Date: July 19, 2020, 8:43 am
---------------------------------------------------------
At some point increasing tyre pressure = more grip, (somewhat
counter intuitive) so may have added to the spoke issue, but
also more rear grip would make the understeer issue worse.
#Post#: 2634--------------------------------------------------
Re: Bugatti Type 37 Build
By: StefanN Date: July 19, 2020, 9:54 am
---------------------------------------------------------
[quote author=ChrisS link=topic=3.msg2632#msg2632
date=1595153513]
What's your weight distribution like? Mine is 70kg rear, 35kg
front, so exactly 2:1.
[/quote]
89kg rear 42kg front, so overall a bit more portly but only
slightly more rear biased than yours.
Also, from pictures it looks like I sit further back than you
(and add more weight!)
#Post#: 2652--------------------------------------------------
Re: Bugatti Type 37 Build - tyres
By: StefanN Date: July 22, 2020, 3:13 am
---------------------------------------------------------
Ok, the whole tyre thing is getting more complicated... in
theory
HTML https://www.f1technical.net/forum/viewtopic.php?t=12762
Will be glad to try it out on the track.
#Post#: 2655--------------------------------------------------
Re: Bugatti Type 37 Build
By: RhysN Date: July 22, 2020, 5:00 am
---------------------------------------------------------
Interesting links, but are you really surprised? I could recite
a lengthy story where the same size tyre from different
manufacturers could make a difference of places in a race of
several tens out of 50 odd competitors. Side wall flex, type of
rubber, pressures are only some of the factors.
If it were simple then there would not be millions spent on tyre
technology.
Once upon a time, not long ago it was considered that cornering
or braking forces in excess of 1g were impossible. Now even
non-aero cars are way above that.
*****************************************************
DIR Previous Page
DIR Next Page