Advice sought on fitting a wider rear wheel in my M750.

[utopia]

Well, I've been threatening to do it for some time now .....
I'm after a pair of carbon wheels.

This has been brought forward slightly because I've spotted that HPS have some Dymag CA5 wheels with minor cosmetic defects, for about £1500 a pair.
Trouble is, both Dymag and BST only make std carbon rims in 5.5 and 6.0 widths, whereas my original rear wheel is 4.5.
There will be an ally swingarm from a 900 going on this winter too, so I can probably cover any clearance/fitment issues but my main concern is that the wider rear rim/tyre will slow down the steering, and I would rather no do that.
I would be interested in your thoughts on this, ie how big an effect it might be and how it might perhaps be reduced with other changes to the geometry.
A major feature of the 750 is its flickability and I'm loathe to do anything which might spoil that ... especially if it costs me £1.5k to do so.

There is an alternative though.
Further enquiries revealed that BST will make a 4.5 rim to special order.
No extra charge for it being a special but the price of BSTs is an eye watering £2,300 a pair.
This means that the cost of being fussy about the rim size will be a staggering £800.
On the other hand, £1,500 is a lot to gamble on the Dymags if there is a chance that they wont really be right for the bike.
And at the end of the day, this bike has to be right ... I'm not looking for any compromises.

I have reserved a pair of the Dymags over the weekend while I think about it some more.
Your advice/thoughts would be greatly appreciated.

[slob]

It will feel a little harder to get turned in/more stable in a straight line.You'll want to go from a 120/60 front to a 120/70, which is what the big D fitted to Monsters with a 180 rear.

[utopia]

Thanks Rob.
Do you think the extra slowness of steering and increased straight line stability will ...
a) be within acceptable levels.
b) be possible to correct by lowering the front/raising the rear.

I already have a 170 section front tyre waiting to go on actually.
Trouble is, I bought that in order to try and quicken the steering, so its original purpose will be masked to some extent by the wider rear.

I know its all going to be a bit subjective anyway, and will depend very much on personal preferences, but I'm just trying to get some idea of exactly how much of an effect the bigger rear rim will make, so I can make a choice.

I really quite fancy the Dymags, partly because the tapered spoke design just looks more correct, ie likely to be stronger, than the straighter spokes on the BSTs.
Also, I have discovered that Dymag have reverted to ally hubs rather than using magnesium, with which I believe there were some constructional issues in the past.
On the other hand, BSTs seem to have "the name" and be well proven.

[Dukedesmo]

5.5" rear with a 170 will work fine, can't see it being much slower turn than a 160 on a 4.5" and any difference would be more than compensated by the significant weight reduction IMO.

[slob]

Originally Posted by Dukedesmo

5.5" rear with a 170 will work fine, can't see it being much slower turn than a 160 on a 4.5" and any difference would be more than compensated by the significant weight reduction IMO.

I think he means 120/70 front, not 170/x but I agree the difference won't be huge, especially as you say, with lighter wheels. Even different manufacturers profiles may make a difference where the numbers are the same. 70 section front is common on DD bikes, as big lean angles can run off the edge of a 60 section.

[Yorkie]

I have played about a bit with tyres and wheel widths. The rear on my 1999 Monster is a 900 rim, slightly wider than the normal 600 rim it had. This is wrapped in a 190 Metzeler bit of rubber.

My 1992 Cafe racer thingy has a standard 750 rim and it has a Pirelli 180/55/17 wrapped around it. I have loads of clearance from the swingarm and chain so no dramas with them being fitted.

The handling may be slightly different but not that I noticed it much. On the Monster you can counter the slow turning by fitting the jack up rose joints.

Yorkie

[Mr Gazza]

I can sense your adrenelin, as you poise for the deal....I love the thrill of the chase myself.

Look at it this way....At that price you will almost certainly get you money back if it doesn't work out. You might even make a small profit, if the "cosmetic defects" can be cheaply put right with lacquer, stickers or a clever, carbon revealing paint job (as in Capo's tank).

Worst case scenario, I reckon would be to cost you some strange section tyres. (But you would probably wear them out while you worked out whether you liked the wheels or not...)

[utopia]

Originally Posted by Mr Gazza

I can sense your adrenelin, as you poise for the deal....I love the thrill of the chase myself.

Ha ha ha .... he snorted repeatedly, while pacing around the room a few times, before returning to the keyboard.
I very much recognise that as a comment particular to yourself, and I thank you for it.
And you're dead right ... I'm equally fond of spinning it out and getting the most out of the chase.
But Monday ... I move in for the kiss-off.

I think the Dymags are a no-brainer at that price really.
And that means I have to get them NOW too.

The cosmetic defects are listed as such minor things as maybe an area where the cloth has a bit of a "shake" in the weave, or the lacquer is a bit too thick in small areas.
Not even chips, pinholes or anything else which would compromise them structurally or affect their performance or durability in any way.
And they are confined to the front wheel .. the rears are 100% grade A in every respect.

In a strange way, I'm almost glad that the cosmetic defects are there actually.
For one, the discount price is what is making this happen now, rather than next year ... and what price an extra summer on carbon wheels ?
But more than that, it kinda emphasises that its the engineering and not the bling that I'm doing this for ... which hangs just fine with me, alongside I think around £600 discount (or £750 on prices after January).

And as Capo pointed out, that kind of money would buy a pair of FCR carbs.
I really am forced into buying the Dymags aren't I ... really ... honest ... on Monday ... there's no avoiding the inevitability, even if I were in the remotest way inclined to do so.

Other factors are ...
I get new wheel bearings .. well mine are 20, 000 miles old.
New cush drive.
New sprocket, with the opportunity to make the change down a tooth on the rear that I've been planning for a while now.
Future tyres will be home-fitted, saving me money in the long term.
That's another couple of hundred quid which a creative accountant could knock off the perceived cost of the wheels.

Some might say its sacrilege to cover the carbon but to be honest, I've been considering painting them anyway, even if I was buying perfect ones ... in the same bronze-ish gold of my original wheels.
When the time comes, I might just have to leave them bare though.
But I was thinking that a coat of paint might well be a maintenance aid, because it would allow me to spot any stone chips etc much more easily.
So yes, maybe leaving some carbon showing somewhere.

Anyway, I'm pretty sure that I'll be nipping over to Derby early next week to check out the defects and then, almost certainly, pay the man and go home to wait (not very long at all) for them to arrive ... or even go back and collect if I'm too pumped up by then and can't wait.

Just now I'm rather looking forward to that moment tomorrow morning when, sometime after waking up, I suddenly remember that all this is happening.
I shall probably make a pot of tea in celebration.

[utopia]

Hmmmm... thanks Tim.
I've been veering towards the BSTs rather than risk the downside of the wider rim, but the price is so salty that even with the obsession that I have for this monster, it was all getting a bit unreal since the wheels would be worth more than the rest of the bike.
But yes, I think there is some sense in what you say, ie that the much quicker steering due to the reduced gyroscopic weight will tend to override the slight extra slowness from the wider rim.
I guess there will be a speed related element to that as well, but from here the outcome starts to get a little difficult to predict.
But, phew .... it looks like I might be able to do this for a staggeringly big price ... as opposed to a completely ridiculous one.
I prefer the looks of the Dymags anyway really.

So I think at this point in time that I'm veering back towards the Dymags.
It'll probably be a roller coaster over the weekend though, so bear with me while I blab a lot as my thoughts shift around.
I will be making a decision one way or the other by Monday though.
Any further thoughts would be greatly appreciated in the meantime.

On the plus side, I think I can leave my lightweight, full-floating disc bobbins until later, which saves a few quid I guess, or at least offsets it.
They don't seem all that significant now.

[pompone]

Dunno, I'd probably still go for forged wheels for road use tbh.

[utopia]

We can discuss in the van.

But one way I see it is that I'll never, ever buy carbon wheels for any other bike.
Wouldn't even want to.
Don't and wont feel the same about any other bike.
This will be my only chance.
And I'm happy (keen, even) to protect them by changing my own tyres.
Also my engineering interest is aroused by the potential to make the maximum possible weight saving on the wheels (because its such a critical area and pays such huge dividends in so many ways) and just see what it actually feels like.

There's something of the spirit of that NCR bike that we saw on the EICMA trip too.
That had BST carbons, though I never felt them spin.
It also pulled no punches as far as lightness was concerned ... and felt wonderful for it, even at a standstill.
So its a sentimental, spiritual, arty, cultural thing as well, which pays homage to the spirit of that bike.

And anyway, every now and then you just need to do something .. to the limit.
Its out there.
On the edge.

[Dukedesmo]

You're now powerless to resist it Jeff, go with the flow.

You know it makes sense...

[Darkness]

Originally Posted by utopia

Dymag and BST only make std carbon rims in 5.5 and 6.0 widths, whereas my original rear wheel is 4.5.
There will be an ally swingarm from a 900 going on this winter too, so I can probably cover any clearance/fitment issues but my main concern is that the wider rear rim/tyre will slow down the steering, and I would rather no do that..

I see that NCR do some rather pretty carbon wheels in their catalogue, but they are 3.5 x 17 front and 6.0 x 17 rear.

I'm guessing that the saving on spinning unsprung weight is the huge advantage of the carbon rim and tyre combination and the geometric change is less significant and can be countered by changing trail angles and steering head offset.

I would be inclined to stop at the 5.5 rears though as that is a known starting point from the m900. The 6,0 may need a lot more development to get right?

[utopia]

I daren't look in the NCR catalogue.
Last time I perused their products I spent the next 24hrs seriously considering selling a house to fund a new bike.
Ok, not my actual house that I live in, but the other one that provides virtually all my income.
And 2yrs later, I still have to control the impulse from time to time.

I think you're dead right about being able to tune in the 5.5 rear.
Its a minor gamble, but worth it I think .... and it all adds to the excitement.

I did ponder the 6.0 as it would sit rather nicely alongside my new chrome sissy-bar, and my sick leather tassels ..... er, not.

By the way, it only took me about 30secs to remember when I woke up this morning.
Did a little dance ... hee, hee.

[BigOz]

I'm running a 5.5" rear in place of the 4.5" that came stock and having now run a few different tyre brands and models I've found the difference between tyre brand/model feels greater than the difference going from 120/60 front and 160/60 rear on a 4.5" to a 120/70 front and a 180/55 rear on a 5.5" of the same brand and model.
I did move the fork position in the yokes to maintain the geometry after the tyre size change.