Condensed Answer: Road bikes aren’t optimal for riding on crushed limestone. Nonetheless, they can still perform surprisingly well on such a surface if the rider is aware of the bike’s limitations and takes precautions to avoid technical failures. The most common issues are flat tires, chipped rims and damaged bike paint.
What is crushed limestone?
Crushed limestone is made by breaking mining limestone or dolomite rock deposits with the help of rock crushing machines. Once the stones are broken down, they’re filtered by size.
Crushed limestone has many uses such as:
- Road base
- Railroad ballast
- Back fill retaining walls
Note: The properties of crushed limestone make it a frequently used material for road construction. Therefore, the chances of stumbling on a crushed limestone road when riding your road bike outside of the city are relatively high, especially if you make a detour and switch to smaller roads.
The Problems with Riding a Road Bike on Limestone Roads
There are three main ways to get a flat tire:
- Pinch flat. The inner tube is pressed against the rim when the wheel comes in contact with the edge of an object at a high speed.
- Puncture. An external object pierces the outer tire and then the inner tube.
- Internal flat. A spoke eyelet, a nipple or a spoke pierces the inner tube. The usual causes of an internal flat are excessively long spokes, poorly tensioned spokes, or the absence of a protective rim tape.
Road bikes are a lot more likely to experience pinch and puncture flats than bicycles with fatter tires for the following reasons:
- Thinness. Road bike tires are lighter and thus thinner. This is especially true for the so-called competition tires.
Competition tires are so thin that flats are a very common occurrence even when riding on regular paved roads.
For that reason, it’s highly advisable not to use a competition tire on crushed limestone. If you do, a flat or a series of flats is practically guaranteed.
Conversely, MTB tires are heavier, thicker and more puncture-resistant to match the style of riding and the terrain that MTBs are used on.
- High air pressure
Road bike tires operate at 2-4 times higher air pressure than MTB tires. The high air pressure makes the tires firm and improves their rolling resistance. As a result, it takes less effort to pedal and reach higher speeds.
The high air pressure is beneficial to puncture resistance too. The higher the air pressure, the harder it is to get a pinch flat (regardless of the bike tire).
Also, the higher air pressure makes it more difficult for an external object to pierce the tire thanks to the extra firmness.
However, the high air pressure also prevents the tire from deforming upon meeting an object. As a result, the stress isn’t spread over a larger contact area, and a sharp object can penetrate the tire.
Crushed limestone is made of small stones which have multiple sharp edges. This greatly increases the chances of getting a flat.
The recommended measures to reduce the likelihood of this outcome are:
1. Run the widest possible tires that your frame and fork can operate with while still having a sufficient amount of clearance.
If you have a newer bike, you will more than likely be limited to tires between 25 and 32mm. If you have an older road bike from the late 70s, for example, you may fit even 35mm tires.
The wider tires are not only more resistant to punctures, but they can also operate at lower air pressure and will thus provide more comfort.
That said, it’s totally possible to ride on crushed limestone even with 23-25mm tires. However, the ride will be quite harsh due to the high air pressure.
2. Make sure that the tires have extra puncture resistance. Puncture-resistant models will be heavier than regular ones but the weight penalty is worth it. At the end of the day, it doesn’t matter how fast a bike allegedly is if you spent most of the day on the side of the road playing with tire levers and patches.
3. Use the appropriate air pressure. If you’re unsure go with the higher setting. It’s better to have more air in the tires than not enough. As mentioned, the extra air protects from pinch flats and pushes away external objects.
Frame and Fork Protection
When riding on crushed limestone, the tires will be throwing small stones and debris at the frame and fork persistently. The stones will damage the paint whereas the small debris will make the drivetrain gritty.
Below is a list of tips meant to exercise some damage control:
- Enough clearance
Make sure that the fork and frame offer at least a few millimeters of clearance. Otherwise, small stones may get stuck between the tire and frame/fork. When that happens the tire will push through and scratch the frame/fork with the stone. In extreme cases, the wheel may even seize and cause an accident.
- Frame protection
Frame protection represents thin folio which acts as another outer layer. (It’s frequently) installed on mountain bikes.
It’s a good idea to put frame protection on the downtube, chainstays and the rear of the seat tube.
- Full Fenders
Full fenders will stop a lot of the dirt and rocks thrown by the tires. That said, most road bikes do not have the clearance for full fenders, especially if you upgrade the tires to wider ones.
Fenders help only when they encompass the entire wheel. The two most impart sections are the area between the fork and the rider as well as the one between the rear tire and the seat tube. Clip-on fenders are partial and do nothing for those sections.
- Crank Protection
The crank area near the bottom bracket can also be easily damaged by small tones and occasional contact with the ground. Hence why mountain bikes use crank protectors. To protect your cranks, you may consider a pair.
- Gear Ratio
The rolling resistance on gravel and limestone is higher. Thus, you may find the current gears on your road bike too high to maintain decent cadence. If that’s the case, you may consider adding a cassette/freewheel with a larger rear cog and/or using a smaller chainring at the front.
Summary: What You Need To Know
- Road bikes are not ideal for crushed limestone, but they can offer acceptable performance nonetheless. The smaller and finer the limestone is, the better the experience will be.
- The most common issues are low comfort, flats and damaged paint.
- To reduce the likelihood of a flat it is recommended to run wider tires with puncture resistance at fairly high air pressure.
- To protect the pain, the rider can install frame protective folio and the most frequently damaged areas – downtube, seat tube, chainstays.