Cycling UK Forum

Hi all, I've been lurking here for a while, really enjoying the helpful advice, and thought it was time to sign up and ask a question of my own...

I have a 2011 Pinnacle Lithium hybrid which I use for fairly short leisure rides and occasional commutes. Last time I paid for a service, my LBS warned me that the bike was not up to carrying heavy loads on the back. We have a Roland Add+Bike, which attaches to a specific rack fitted to my bike - the rack is quite heavy, plus there is the load from the trailer bike to consider. I am also considering fitting a rack mounted child seat for our youngest.

I have identified two areas of weakness that I can do something about:
1) the rear wheel is only 32-spoke; and
2) the drivetrain has a freewheel, rather than a freehub and cassette.
Clearly, both can be addressed in one go.

My question is, should I be looking at upgrading the rest of the drivetrain at the same time? Current gearing is 3x7, which is fine, but 7 speed cassettes look to be a bit thin on the ground. Would I be better off moving to 3x8 or 3x9? In order to keep costs down, could I get a 3x8 freehub, and fit a 7 speed cassette with a spacer (allowing me to keep the 7 speed shifters for the time being)? I am probably looking at moving up to Deore quality.

If you want a really strong wheel, a 7s hubbed wheel will always have less dish than an 8s hubbed wheel, and will therefore be much stronger. You can usually simply delete one cog from an 8s cassette to make a 7s one if you need to. If you go with 7s and the freehub body fails then you should be able to fit an 8s body to a 7s hub and redish the wheel to suit. But (provided you keep the water out of it) it might take 10 years to wear out a 7s freehub body, so it shouldn't be a major worry.

cheers

The rear wheel could be upgraded to 36 spoke 9sp Deore freehub.
An 8sp cassette would then fit straight on.
The magic is that your 7sp shifters will work perfectly with and 8sp cassette but you'll only be able to use 7 of the 8speeds.

With the kind of load you mention I'd have a handbuilt wheel built by Spa Cycles with a Sputnik rim for extra strength:- http://www.spacycles.co.uk/products.php ... b0s176p349

Thanks guys,
After further research, it seems that it is 7-speed freehubs which are hard to get hold of. I guess I therefore need to get an 8/9 speed freehub, and accept the loss of strength from the extra dish. I will probably stick with a 7-speed cassette, as I understand that there is a slight loss of performance using an 8-speed cassette. Shelton Brown says I will need a 3.5mm spacer.

Would others agree with the Sputnik recommendation? They seem very cheap, and heavy too, which will reduce braking performance. I guess that is the price you pay for strength though.

mike_dowler wrote:Thanks guys,
After further research, it seems that it is 7-speed freehubs which are hard to get hold of.

really?

http://www.chainreactioncycles.com/shimano-rsx-a410-rear-hub/rp-prod87011

at that price, buy two, if you are worried about spares down the line. BTW the axle will be long enough to respace to 130mm if you want to.

Would others agree with the Sputnik recommendation? They seem very cheap, and heavy too, which will reduce braking performance. I guess that is the price you pay for strength though.

sputniks are fine. There are plenty of lighter rims, but they will wear out on the braking surface before a sputnik.

I don't think you need to worry about a 'reduction in the braking performance because of the weight', we are not talking F1 cars here....

cheers

Plus 1 for the Sputniks hand built from Spa.

I have my 7 speed cassette on a 36 spoke setup.

With spacer.

Agree totally that it's a sod/insane that you have to use an 8-speed dish when all you want is 7 speed which is fine for me.

Thanks Brucey and Portland

mike_dowler wrote:Thanks guys,
After further research, it seems that it is 7-speed freehubs which are hard to get hold of. I guess I therefore need to get an 8/9 speed freehub, and accept the loss of strength from the extra dish.

Which is minimal,think how many fully loaded touring bikes there are,running 9sp cassettes without a problem.

I will probably stick with a 7-speed cassette, as I understand that there is a slight loss of performance using an 8-speed cassette.

Someone will have to explain that to me

(Sputniks)seem very cheap,and heavy too

This is one case where cheap doesn't equal nasty but durable and long lasting.

which will reduce braking performance.

something else that'll need explaining to me

I guess that is the price you pay for strength though.

sputniks=bombproof and are one of the most durable rims on the market despite being cheap as chips

Brucey wrote:

mike_dowler wrote:Thanks guys,
After further research, it seems that it is 7-speed freehubs which are hard to get hold of.

really?
http://www.chainreactioncycles.com/shimano-rsx-a410-rear-hub/rp-prod87011

at that price, buy two, if you are worried about spares down the line. BTW the axle will be long enough to respace to 130mm if you want to.

cheers

Those RSX are only 126mm OLN.
I presume, as it's an "hybrid" bike, that it will be 135mm OLN?
Therefore I wouldn't worry about the dishing using an 8/9 speed hub with a spacer for the 7 speed cassette.
+1 for 36 spoke Sputnick/Deore.

cycleruk wrote: I presume, as it's an "hybrid" bike, that it will be 135mm OLN?

well I dunno; if it is a tourney drivetrain, would it have been 135mm oln with a 7s screw-on freewheel?

Need to measure it to be sure I guess.

cheers

Reohn, just to explain myself:

1) my understanding (but pls correct me if this is incorrect) is that the spacing of an 8s cassette is slightly smaller than that of a 7s. Thus, the indexing will be slightly non-optimal.

2) I think I'm on stronger ground here - a heavy rim acts as a flywheel, with a proportionally higher angular momentum for a given speed. More torque is therefore required to slow the wheels.

With a small allowance for the spokes etc there is about 3lbs of weight in each rim and tyre etc and it is moving at the same speed as the bike. So that is 6lbs at (say) 20 mph. Compare that with the linear inertia of the bike and rider which might be 200lbs at 20mph. So the flywheel effect of the wheels might consume about 3% of the total braking effort.

Supposing you bought very light wheels which are still (just) strong enough for the task in hand. You might reduce the weight in each wheel by 1 lb. Even allowing for the fact that the weight in the wheels 'counts double' because it has linear inertia and a flywheel component, you have only reduced your braking effort by about 2%.

Maybe 2% is significant for some folk. But I'd say that unless you are racing, maybe not, especially if it comes with a penalty of reduced durability.

BTW you meed to measure your rear hub width; yours could be 126mm, 130mm or 135mm. This will affect wheel dish, strength and hub choices.

cheers

mike_dowler wrote:Reohn, just to explain myself:

1) my understanding (but pls correct me if this is incorrect) is that the spacing of an 8s cassette is slightly smaller than that of a 7s. Thus, the indexing will be slightly non-optimal.

The spacing difference between 7&8sp cassettes is 0.2mm(5mm for 7sp,4.8mm for 8sp)which over the 7spaces between and 8sp cassette is 0.2x7=1.4mm,forgetting the space between top and 7th,because the rear mech releases cable tension against the mech limit screw,that then leaves us with a 1.2mm difference over the six remaining gaps/spaces.
I've on a couple of occasions laid the six riveted cogs of a Shimano 8speed cassette and the same six of a 7sp cassette flat on the bench side by side and found no difference when a straight edge is laid across both.
I've also run an 8sp cassette with 7sp STI's and 7sp down tube shifters and found they shift perfectly .
So in theory you are correct but in practice..............

2) I think I'm on stronger ground here - a heavy rim acts as a flywheel, with a proportionally higher angular momentum for a given speed. More torque is therefore required to slow the wheels.

Brucey's answered that question far better than I ever could.

Brucey wrote:

mike_dowler wrote:Thanks guys,
After further research, it seems that it is 7-speed freehubs which are hard to get hold of.

really?

http://www.chainreactioncycles.com/shimano-rsx-a410-rear-hub/rp-prod87011

at that price, buy two, if you are worried about spares down the line. BTW the axle will be long enough to respace to 130mm if you want to...................

Yes I bought a couple of these. When the round tuit that I have on order turns up I'm going to put a longer axle in and respace them to 135mm. With 8 speed Claris shifters (I agree with the comments about 8 speed shifters coping with 7 speed spacing) I can have an almost dishless 3x7 13-34 transmission without any bodging. Perhaps I ought to but some more while I can!

edit for typo