Wheel advice: 1.85 or 2.15. What's best? Lightest?

[gavinnz]

Hello Bucket people!

I am not a buckect racer.. but I did "race" a 1954 175 MV Agusta in the classics a few times just for fun.... I even have a thrid place plaque!!!! And YES their WAS three people in my class in that race.

Anywho... my question for the collective wisdom of the group is this....

What are the lightest cast rims avalible here in NZ that are front 1.85/17 and rear 2.15/17.??
I am at the moment looking at wheels from a FXR150.... are their lighter ones in those sizes??

I am building a Gilera Saturno based 558cc superlight special and I want narrower lighter rims and tyres as the orignals are way to large. Looking at fiting 90/80/17 front and 110/80/17 Michelin Pilot Sporty tyres.

Regards
Gavin

"Gilera Saturno 558 Superleggera"

[jasonu]

Hello Bucket people!

I am not a buckect racer.. but I did "race" a 1954 175 MV Agusta in the classics a few times just for fun.... I even have a thrid place plaque!!!! And YES their WAS three people in my class in that race.

Anywho... my question for the collective wisdom of the group is this....

What are the lightest cast rims avalible here in NZ that are front 1.85/17 and rear 2.15/17.??
I am at the moment looking at wheels from a FXR150.... are their lighter ones in those sizes??

I am building a Gilera Saturno based 558cc superlight special and I want narrower lighter rims and tyres as the orignals are way to large. Looking at fiting 90/80/17 front and 110/80/17 Michelin Pilot Sporty tyres.

Regards
Gavin

"Gilera Saturno 558 Superleggera"

Not sure about the 'collective wisdom' thing but would like to see some pix of your bike.

[Henk]

You might not have a lot of joy getting an answer here, those look like the stock FXR rim sizes but most of the wheel conversions done on buckets are to go to wider rims to run cast off 125GP slicks. I would check the std rim sizes but I seem to have sold off or passed on all the stock wheels I had. In those sizes I doubt you'll find much in the way of light rims, they seem to be fitted to committed hacks where performance isn't a prime consideration. RGV150 spoked wheels may be your best bet though.

[gavinnz]

Thanks for that tip. I just spent a good half hour researching the RGV150. Seemed like a good option but I could not find if they make a disc brake back wheel in a wire spoke type. Seems maybe not.

I was at one stage looking at new Morad rims from Spain and Talon hubs... but the cost is high and in the end I have no facts about the end weight of the wheel compared to a cast aluminum item of the same size.

I have not found concrete facts on the weight of a cast aluminum or magnesium wheels vis wire spokewith the best bits ftted.... just LOTS of uninformed people making statements both ways with no back up in fact. Frustrating!

Regards
Gavin

[gavinnz]

Not sure about the 'collective wisdom' thing but would like to see some pix of your bike.

It's not much to look at overall as it's a work in progress.
I am using it as a thinking excersise to force myself to think outside the square and find interesting ways to save weight on the bike..... I keep a notebook with every gram saved listed!
It's nice to break away from the "should keep things original" mindset and get creative


I aill start a flicker page soon and upload some photos to that and post a link.

Regards
Gavin

[F5 Dave]

I think you should start out by considering what tyres you are going to run, which you seem to have done & then run the recommended rim width for those tyres. a 90 front tyre should be run on a 2.5" rim, though you can get away with a 2.15". Any narrower & you are folding the tyre over & putting less rubber on the road.

RGV150 rims are woefully narrow.

Rear: Hmm. A 558 single. If fairly stock you're looking at say 35hp & warm to road hot 60. At the top end I'd want to run same size rear as a 250 2 stroke. Which is a 150 on a 4.5" rim. & at that stage I'd reevaluate the front to a 3" & 110. If a low powered bike the rear could pull a 130 on a 3.5.

I'd look to TZR/FZR, RGV rims as most suitable. Come in different widths over the years. They do have over engineered heavier cush drives that may seem necessary for a stroker, but for a single this would be totally required so live with it.

[gavinnz]

I think you should start out by considering what tyres you are going to run, which you seem to have done & then run the recommended rim width for those tyres. a 90 front tyre should be run on a 2.5" rim, though you can get away with a 2.15". Any narrower & you are folding the tyre over & putting less rubber on the road.

Rear: Hmm. A 558 single. If fairly stock you're looking at say 35hp & warm to road hot 60. At the top end I'd want to run same size rear as a 250 2 stroke. Which is a 150 on a 4.5" rim. & at that stage I'd reevaluate the front to a 3" & 110. If a low powered bike the rear could pull a 130 on a 3.5.

Can you explain why I need tyres that wide?
Heat build up? Grip under brakes or power? Contact patch when cornering?

I am looking for facts, not just what fashion and racing has told us is the "best" for the road.
Manx Norton racers have narrow tyres and they get huge lean angles and speed on the racetrack on modern treaded rubber.... I appreciate the fast Manx guys use 18 inch tyres and hence get more rubber down than a 17 inch in the same profile... but I would not be going as hard as them either.

My 1970's 230KG Italian touring bike has a 100/90 front....
My 1970's 750cc, 200kg Italian Sports bike has a 110/90 rear... and they handle well and I have never had a tyre slide.

Here is part of a tyre to rim chart... the tyres on the left and the recommended rim on the right.
It seems that the rims size for the front 1.85 for a 90/80/17 is fine and the 2.15 for a 110/80/17 is just outside whats recommended, BUT I have varous places and people teling me they have done that and it works very well. Michelin recommend their Pilot Sporty 110/80/17 tyre for bikes with 2.15 rims.

90/80*17 1.85/2.15/2.50
90/90*17
90/100*17

100/100*17 2.15/2.50/2.75
100/90*17
100/80*17
110/90*17

100/70*17 2.50/2.75/3.00
110/80*17

I really am asking a qenuine questions and I want to know what I am missing!!
Regards
Gavin

[F5 Dave]

Well what are you trying to do with it? a tootle around bike? what sort of power are you expecting & what sort of riding? The more sporty the tyre the closer it becomes to a slick profile. Older style tyres ballooned out somewhat & run skinny rims.

So yeah use what the tyre manufacturer recommends. Classic race bikes probably use imported race tyres unlike what you can buy for the road, I couldn't tell you, but Avon for example use to make AM series tyres for racing that looked like the road ones but were different compound.

So what are you trying to build? What sort of power & what sort of riding? Old Guzzis run on very skinny tyres, but put out meager levels of power & just aren't meant for scratching. Not to be said that I've seen some well ridden ones on crappy old Conti joke tyres.


Power requires more rubber. For example I'd ridden for years using 90 front slick tyres on the back on my 50 racer. We're talking less than 15hp here. To push to the next level I moved up to 115s & realised what I had been missing.

Now that is flat out at the front of the field. So how much power are you going to put down & how hard are you going to be turning the handle when leant way over? I thought leant was a good enough word, but seemingly my PC doesn't. I won't argue.

[gavinnz]

Power requires more rubber. For example I'd ridden for years using 90 front slick tyres on the back on my 50 racer. We're talking less than 15hp here. To push to the next level I moved up to 115s & realised what I had been missing.

You seem to be a knowledgeable chap. Can you put in words why exactly more power requires more rubber? I don't disagree at all, I am just wondering how much they apply or don't to a given bike.

Just thinking out loud..... If say the bike came from the factory with tyres that were dictated more by fashion than real world dynamics, (as I believe my Saturno was with 140 rear) then more power in the same chassis might in fact still mean smaller tyres are going to give the same level of grip with less rotating mass and a contact patch closer to the centre line of the bike.

And what was it you were missing exactly? Were you smaller tyres getting to hot? Spinning up? The devil is in the detail!

I have had a simpler conversation on an Chassis Design forum so I will post some messages here that might be of interest to the subject....

Interesting stuff.

As for the bikes use.... not a race bike. A light weight (aiming for 110kg without gas) tight road bike and maybe the odd track day fun bike.
Regards
Gavin

[gavinnz]

one guys thoughts..... not me.

"Contrary to popular (read: squid kids on sportbikes) opinion, narrower tires make for easier and more neutral handling. IMHO: use the narrowest tire that you can get away with. If your bike will not spin up the rear wheel by getting hard on the gas while leaned over, it has too much tire. This says as much about the rider and riding style as it does about the bike's HP and suspension. Why put more tire under the bike than the rider is willing to use? Why not trade the excess capacity for benefits in neutral handling? This might be a heretical idea... but it's worth opening for discussion."

[gavinnz]

This was my post to the chassis group....

Ok this might end up getting quite technical...

Modern bikes have very wide tyres.
Now why is that?
I can see that a large heavy powerful bike would use a larger area to help
dissipate heat and have a larger over all area so wear would distributed
more hence slower over all tyre wear. And with heaps of power a larger
surface area in contact with the road in a staight line (with a soft
compound) would give more grip for acceleration without wheel spin, and more
contact patch for braking.

What I am thinking about is.... does a wider tyre really give you that much
more contact patch when cornering? I am thinking about the way a tyre rolls
into a corner and I can't see how a wider tyre would give much more surface
area in contact with the road when lent right over in a corner?

If you are running a large single cylinder engine in a light weight bike
where heat build up, wear and wheel spin are not factors then can you fit
good narrower tyres without compromising handing and grip to a huge extent?

On my Gilera Saturno they have 110/70/17 and 140/70/17 tyres. I am wondering
how much of that tyre choice was really late 1980's fashion and not sound
motorcycle engineering. After all not long before that a 110 or 120 tyre was
considered fine for the back of a big bore sports bike on the '70's.
The wider the tyre the further away the contact patch is from the centre
line of the bike.

Their is also the compound of tyres in relation to their contact patch size
that I have been thinking about. A large tyre would need to be softer as the
pressure per square inch would be less than a narrower tyre that could be
harder compound but have the same real grip as it is being pressed into the
road suface harder per square inch.

In the classic racing they get HUGE lean angles on very narrow tyres.
So what gives? What am I missing the point of?

Regards
Gavin

[RDjase]

This was my post to the chassis group....

Ok this might end up getting quite technical...

Modern bikes have very wide tyres.
Now why is that?
I can see that a large heavy powerful bike would use a larger area to help
dissipate heat and have a larger over all area so wear would distributed
more hence slower over all tyre wear. And with heaps of power a larger
surface area in contact with the road in a staight line (with a soft
compound) would give more grip for acceleration without wheel spin, and more
contact patch for braking.

What I am thinking about is.... does a wider tyre really give you that much
more contact patch when cornering? I am thinking about the way a tyre rolls
into a corner and I can't see how a wider tyre would give much more surface
area in contact with the road when lent right over in a corner?

If you are running a large single cylinder engine in a light weight bike
where heat build up, wear and wheel spin are not factors then can you fit
good narrower tyres without compromising handing and grip to a huge extent?

On my Gilera Saturno they have 110/70/17 and 140/70/17 tyres. I am wondering
how much of that tyre choice was really late 1980's fashion and not sound
motorcycle engineering. After all not long before that a 110 or 120 tyre was
considered fine for the back of a big bore sports bike on the '70's.
The wider the tyre the further away the contact patch is from the centre
line of the bike.

Their is also the compound of tyres in relation to their contact patch size
that I have been thinking about. A large tyre would need to be softer as the
pressure per square inch would be less than a narrower tyre that could be
harder compound but have the same real grip as it is being pressed into the
road suface harder per square inch.

In the classic racing they get HUGE lean angles on very narrow tyres.
So what gives? What am I missing the point of?

Regards
Gavin

Alex/ Ridelife on here has German Heidenau tyres in Dot legal race compound available in narrow sizes. Nice and sticky as we run them on our StreetStock 150 Kawasaki's with 1.6x17 front and 1.85x18 rear rims


Also I think wire wheel RGV150 has 18inch rear

[speedpro]

"IF" wider tyres aren't really a hindrance then using them may be good from a budget perspective. Sure you can get the little sticky tyres and I agree with every reason you have given for using them, BUT, you could end up spending $$$ to be 100% correct when an off the shelf wider tyre from the bike shop may save lots of $$ and be 90% correct. Honestly I haven't checked the price of the little sticky skinny tyres lately but being probably low volume I expect they'll be pricey.
If I remember back to the mid 70s, to get decent contact patches when leaned over the older narrower tyres had a triangular profile which wasn't ideal when transitioning from upright to lean. Dunlop had a tyre that was practically flat each side. You were either upright or leaned over. Whilst leaned over you could apply power but in a not-quite-leaned-over position you were a bit limited. Newer wider tyres with the more rounded profile are way more versatile in this regard.
I run a FZR250 chassis with stock rims, 2.75(F) X 17 and 3.5(R) X 17. I haven't noticed much of a problem with handling.

[jasonu]

I am looking for facts, not just what fashion and racing has told us is the "best" for the road.

Regards
Gavin

Well if you are looking for facts you definitely came to the wrong place.

[gavinnz]

"IF" wider tyres aren't really a hindrance then using them may be good from a budget perspective. Sure you can get the little sticky tyres and I agree with every reason you have given for using them, BUT, you could end up spending $$$ to be 100% correct when an off the shelf wider tyre from the bike shop may save lots of $$ and be 90% correct. Honestly I haven't checked the price of the little sticky skinny tyres lately but being probably low volume I expect they'll be pricey.
I run a FZR250 chassis with stock rims, 2.75(F) X 17 and 3.5(R) X 17. I haven't noticed much of a problem with handling.

Thanks for the input! What size tyres do you run on those rims??

The tyres I am looking at the Michelin Pilot Sporty are $100 and $129 at the moment. So price is no biggie. Not sure about the super sticky race tyres but I will not need those anyway!

regards
Gavin